1. Field of the Invention
The present invention relates to a photosensitive resin composition using a polyurethane resin which is obtained by urethanization reaction without any catalyst followed by reaction with a cyclic acid anhydride and is soluble in aqueous alkali solution, and a manufacturing method of the curing product thereof. More specifically, the present invention relates to a resin composition to provide a curing product having excellent properties including such as developing property, flexibility, adhesion property, soldering heat resistance, chemical resistance, plating resistance and high insulation, etc. is useful for such as a solder mask for flexible print wiring board; an insulation film between layers for multilayer print wiring board; photosensitive light guide; and a manufacturing method of a curing product thereof; and to provide a base material and the like having a layer of the curing product.
2. Description of the Related Art
Conventionally, some part of print wiring board for personal use and most of print wiring board for industrial use are solder masks utilizing photolithograph. More specifically, an image is created by developing treatment after curing with exposure, and a photocuring composition which is finished with hardening with further heat and/or photo irradiation is used. A liquid composition for solder mask, which is a kind of alkali development using a diluted aqueous alkali solution as a developing solution, is mainly used because of environmental concerns. For example, a solder mask composition, as a liquid composition for solder mask which is an alkali development-type and uses a diluted aqueous alkali solution, comprising a photosensitive resin which is produced by addition of acid anhydride to the reaction product of novolac type epoxy resin and an unsaturated monobasic acid, a photopolymerization initiator, a crosslinking agent, and an epoxy resin has been disclosed. (Reference Patent 1, etc.) The curing product of the composition, however, is hard so that when it is applied to a Ball Grid Array (BGA) base board and a flexible base board, which recently are being used in many fields including portable equipments, unfortunately it causes a crack on the surface or it cannot afford a bending property.
Another composition including such as a polybasic acid anhydride modified epoxy acrylate resin produced by the reaction of the polybasic acid anhydride and the reaction product of polyfunctional bisphenol epoxy resin and (meth)acrylic acid, and an urethane acrylate has been disclosed as a material applicable to a BGA base board or a flexible base board in Reference Patent 2. When this is used, it cannot yet afford satisfactory flexibility and it cannot follow against extreme bending even though durability against cracking on the surface is improved.
Further, another resin composition which includes a urethane resin containing unsaturated group produced by a reaction of an unsaturated resin containing hydroxy group, which is produced by a reaction of 0.8 to 1.2 mole of an ethylenically unsaturated carboxylic acid having average molecular weight between 72 and 1000 containing average one carboxylic group and average one ethylenically unsaturated group in one molecule to one mole of epoxy group of diepoxide; a diol compound containing a carboxyl group; a diisocyanate compound; and a polyol compound as appropriate; has been disclosed in Reference Patent 3 and 4. However, if molecular weight is increased, the acid value of the resin also increases in a basis of resin design, and if a content of an ethylenically unsaturated group is increased to increase sensitivity, the acid value of the resin decreases, and therefore, because of such reason, it is difficult to get a well balanced molecular weight, sensitivity and developing property, and an optimization of the solder mask composition is problematic.
Photopolymeric resin composition which includes a urethane modified acid additional vinylester resin obtained by addition of polybasic acid anhydride to an urethane modified vinylester resin composed of vinylester resin obtained by a reaction of an epoxy compound including more than 1.2 epoxy group in one molecule and unsaturated monobasic acid has been disclosed in Reference Patent 5, but it has problematic electric property such as poor insulation property of its curing product, because urethane modified vinylester resin is produced by using a catalyst when the urethane is produced.    [Reference Patent 1] Japanese Laid Open Patent S61-243869    [Reference Patent 2] Japanese Patent 2868190    [Reference Patent 3] Japanese Laid Open Patent 2001-33959    [Reference Patent 4] Japanese Laid Open Patent 2001-33960    [Reference Patent 5] Japanese Laid Open Patent H9-52925
A highly precise and highly condensed print wiring board is demanded to minimize the size of portable equipment and increase communication speed. Accordingly higher grade solder mask is also demanded with maintaining more flexible property to increase electric properties such as gold plating resistance, electroless gold plating resistance, tin plating resistance, board adhesion property and high insulation property. Nonetheless the present known solder mask cannot satisfy these demands.